/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

/*
 * Copyright 2014 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.netty.handler.codec.http2;

import io.netty.util.AsciiString;
import io.netty.util.internal.ConstantTimeUtils;
import io.netty.util.internal.PlatformDependent;

final class HpackUtil
{
    /**
     * Compare two {@link CharSequence} objects without leaking timing
     * information.
     * <p>
     * The {@code int} return type is intentional and is designed to allow
     * cascading of constant time operations:
     * 
     * <pre>
     * String s1 = "foo";
     * 
     * String s2 = "foo";
     * 
     * String s3 = "foo";
     * 
     * String s4 = "goo";
     * 
     * boolean equals = (equalsConstantTime(s1, s2)
     *         & equalsConstantTime(s3, s4)) != 0;
     * </pre>
     * 
     * @param s1 the first value.
     * @param s2 the second value.
     * @return {@code 0} if not equal. {@code 1} if equal.
     */
    static int equalsConstantTime(CharSequence s1, CharSequence s2)
    {
        if (s1 instanceof AsciiString && s2 instanceof AsciiString)
        {
            if (s1.length() != s2.length())
            {
                return 0;
            }
            AsciiString s1Ascii = (AsciiString) s1;
            AsciiString s2Ascii = (AsciiString) s2;
            return PlatformDependent.equalsConstantTime(s1Ascii.array(),
                    s1Ascii.arrayOffset(), s2Ascii.array(),
                    s2Ascii.arrayOffset(), s1.length());
        }

        return ConstantTimeUtils.equalsConstantTime(s1, s2);
    }

    // Section 6.2. Literal Header Field Representation
    enum IndexType {
        INCREMENTAL, // Section 6.2.1. Literal Header Field with Incremental
                     // Indexing
        NONE, // Section 6.2.2. Literal Header Field without Indexing
        NEVER // Section 6.2.3. Literal Header Field never Indexed
    }

    // Appendix B: Huffman Codes
    // http://tools.ietf.org/html/rfc7541#appendix-B
    static final int[] HUFFMAN_CODES =
    { 0x1ff8, 0x7fffd8, 0xfffffe2, 0xfffffe3, 0xfffffe4, 0xfffffe5, 0xfffffe6,
            0xfffffe7, 0xfffffe8, 0xffffea, 0x3ffffffc, 0xfffffe9, 0xfffffea,
            0x3ffffffd, 0xfffffeb, 0xfffffec, 0xfffffed, 0xfffffee, 0xfffffef,
            0xffffff0, 0xffffff1, 0xffffff2, 0x3ffffffe, 0xffffff3, 0xffffff4,
            0xffffff5, 0xffffff6, 0xffffff7, 0xffffff8, 0xffffff9, 0xffffffa,
            0xffffffb, 0x14, 0x3f8, 0x3f9, 0xffa, 0x1ff9, 0x15, 0xf8, 0x7fa,
            0x3fa, 0x3fb, 0xf9, 0x7fb, 0xfa, 0x16, 0x17, 0x18, 0x0, 0x1, 0x2,
            0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x5c, 0xfb, 0x7ffc, 0x20,
            0xffb, 0x3fc, 0x1ffa, 0x21, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62,
            0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
            0x6e, 0x6f, 0x70, 0x71, 0x72, 0xfc, 0x73, 0xfd, 0x1ffb, 0x7fff0,
            0x1ffc, 0x3ffc, 0x22, 0x7ffd, 0x3, 0x23, 0x4, 0x24, 0x5, 0x25, 0x26,
            0x27, 0x6, 0x74, 0x75, 0x28, 0x29, 0x2a, 0x7, 0x2b, 0x76, 0x2c, 0x8,
            0x9, 0x2d, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7ffe, 0x7fc, 0x3ffd,
            0x1ffd, 0xffffffc, 0xfffe6, 0x3fffd2, 0xfffe7, 0xfffe8, 0x3fffd3,
            0x3fffd4, 0x3fffd5, 0x7fffd9, 0x3fffd6, 0x7fffda, 0x7fffdb,
            0x7fffdc, 0x7fffdd, 0x7fffde, 0xffffeb, 0x7fffdf, 0xffffec,
            0xffffed, 0x3fffd7, 0x7fffe0, 0xffffee, 0x7fffe1, 0x7fffe2,
            0x7fffe3, 0x7fffe4, 0x1fffdc, 0x3fffd8, 0x7fffe5, 0x3fffd9,
            0x7fffe6, 0x7fffe7, 0xffffef, 0x3fffda, 0x1fffdd, 0xfffe9, 0x3fffdb,
            0x3fffdc, 0x7fffe8, 0x7fffe9, 0x1fffde, 0x7fffea, 0x3fffdd,
            0x3fffde, 0xfffff0, 0x1fffdf, 0x3fffdf, 0x7fffeb, 0x7fffec,
            0x1fffe0, 0x1fffe1, 0x3fffe0, 0x1fffe2, 0x7fffed, 0x3fffe1,
            0x7fffee, 0x7fffef, 0xfffea, 0x3fffe2, 0x3fffe3, 0x3fffe4, 0x7ffff0,
            0x3fffe5, 0x3fffe6, 0x7ffff1, 0x3ffffe0, 0x3ffffe1, 0xfffeb,
            0x7fff1, 0x3fffe7, 0x7ffff2, 0x3fffe8, 0x1ffffec, 0x3ffffe2,
            0x3ffffe3, 0x3ffffe4, 0x7ffffde, 0x7ffffdf, 0x3ffffe5, 0xfffff1,
            0x1ffffed, 0x7fff2, 0x1fffe3, 0x3ffffe6, 0x7ffffe0, 0x7ffffe1,
            0x3ffffe7, 0x7ffffe2, 0xfffff2, 0x1fffe4, 0x1fffe5, 0x3ffffe8,
            0x3ffffe9, 0xffffffd, 0x7ffffe3, 0x7ffffe4, 0x7ffffe5, 0xfffec,
            0xfffff3, 0xfffed, 0x1fffe6, 0x3fffe9, 0x1fffe7, 0x1fffe8, 0x7ffff3,
            0x3fffea, 0x3fffeb, 0x1ffffee, 0x1ffffef, 0xfffff4, 0xfffff5,
            0x3ffffea, 0x7ffff4, 0x3ffffeb, 0x7ffffe6, 0x3ffffec, 0x3ffffed,
            0x7ffffe7, 0x7ffffe8, 0x7ffffe9, 0x7ffffea, 0x7ffffeb, 0xffffffe,
            0x7ffffec, 0x7ffffed, 0x7ffffee, 0x7ffffef, 0x7fffff0, 0x3ffffee,
            0x3fffffff // EOS
    };

    static final byte[] HUFFMAN_CODE_LENGTHS =
    { 13, 23, 28, 28, 28, 28, 28, 28, 28, 24, 30, 28, 28, 30, 28, 28, 28, 28,
            28, 28, 28, 28, 30, 28, 28, 28, 28, 28, 28, 28, 28, 28, 6, 10, 10,
            12, 13, 6, 8, 11, 10, 10, 8, 11, 8, 6, 6, 6, 5, 5, 5, 6, 6, 6, 6, 6,
            6, 6, 7, 8, 15, 6, 12, 10, 13, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
            7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 7, 8, 13, 19, 13, 14, 6, 15, 5,
            6, 5, 6, 5, 6, 6, 6, 5, 7, 7, 6, 6, 6, 5, 6, 7, 6, 5, 5, 6, 7, 7, 7,
            7, 7, 15, 11, 14, 13, 28, 20, 22, 20, 20, 22, 22, 22, 23, 22, 23,
            23, 23, 23, 23, 24, 23, 24, 24, 22, 23, 24, 23, 23, 23, 23, 21, 22,
            23, 22, 23, 23, 24, 22, 21, 20, 22, 22, 23, 23, 21, 23, 22, 22, 24,
            21, 22, 23, 23, 21, 21, 22, 21, 23, 22, 23, 23, 20, 22, 22, 22, 23,
            22, 22, 23, 26, 26, 20, 19, 22, 23, 22, 25, 26, 26, 26, 27, 27, 26,
            24, 25, 19, 21, 26, 27, 27, 26, 27, 24, 21, 21, 26, 26, 28, 27, 27,
            27, 20, 24, 20, 21, 22, 21, 21, 23, 22, 22, 25, 25, 24, 24, 26, 23,
            26, 27, 26, 26, 27, 27, 27, 27, 27, 28, 27, 27, 27, 27, 27, 26, 30 // EOS
    };

    static final int HUFFMAN_EOS = 256;

    private HpackUtil()
    {
        // utility class
    }
}
